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Li Huafei 091283e3d5 perf probe: Fix NULL pointer dereference in convert_variable_location() 
[ Upstream commit 3cb17cce1e ]

If we just check whether the variable can be converted, 'tvar' should be
a null pointer. However, the null pointer check is missing in the
'Constant value' execution path.

The following cases can trigger this problem:

	$ cat test.c
	#include <stdio.h>

	void main(void)
	{
	        int a;
	        const int b = 1;

	        asm volatile("mov %1, %0" : "=r"(a): "i"(b));
	        printf("a: %d\n", a);
	}

	$ gcc test.c -o test -O -g
	$ sudo ./perf probe -x ./test -L "main"
	<main@/home/lhf/test.c:0>
	      0  void main(void)
	         {
	      2          int a;
	                 const int b = 1;

	                 asm volatile("mov %1, %0" : "=r"(a): "i"(b));
	      6          printf("a: %d\n", a);
	         }

	$ sudo ./perf probe -x ./test -V "main:6"
	Segmentation fault

The check on 'tvar' is added. If 'tavr' is a null pointer, we return 0
to indicate that the variable can be converted. Now, we can successfully
show the variables that can be accessed.

	$ sudo ./perf probe -x ./test -V "main:6"
	Available variables at main:6
	        @<main+13>
	                char*   __fmt
	                int     a
	                int     b

However, the variable 'b' cannot be tracked.

	$ sudo ./perf probe -x ./test -D "main:6 b"
	Failed to find the location of the 'b' variable at this address.
	 Perhaps it has been optimized out.
	 Use -V with the --range option to show 'b' location range.
	  Error: Failed to add events.

This is because __die_find_variable_cb() did not successfully match
variable 'b', which has the DW_AT_const_value attribute instead of
DW_AT_location. We added support for DW_AT_const_value in
__die_find_variable_cb(). With this modification, we can successfully
track the variable 'b'.

	$ sudo ./perf probe -x ./test -D "main:6 b"
	p:probe_test/main_L6 /home/lhf/test:0x1156 b=\1:s32

Fixes: 66f69b2197 ("perf probe: Support DW_AT_const_value constant value")
Signed-off-by: Li Huafei <lihuafei1@huawei.com>
Tested-by: Arnaldo Carvalho de Melo <acme@redhat.com>
Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Cc: Frank Ch. Eigler <fche@redhat.com>
Cc: Jianlin Lv <jianlin.lv@arm.com>
Cc: Jiri Olsa <jolsa@redhat.com>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Masami Hiramatsu <mhiramat@kernel.org>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Srikar Dronamraju <srikar@linux.vnet.ibm.com>
Cc: Yang Jihong <yangjihong1@huawei.com>
Cc: Zhang Jinhao <zhangjinhao2@huawei.com>
http://lore.kernel.org/lkml/20210601092750.169601-1-lihuafei1@huawei.com
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>
2021-06-10 13:39:17 +02:00
arch MIPS: ralink: export rt_sysc_membase for rt2880_wdt.c 2021-06-03 09:00:50 +02:00
block blk-mq: Swap two calls in blk_mq_exit_queue() 2021-05-19 10:13:14 +02:00
certs certs: Fix blacklist flag type confusion 2021-03-04 11:37:59 +01:00
crypto async_xor: increase src_offs when dropping destination page 2021-05-14 09:49:59 +02:00
Documentation Documentation: seccomp: Fix user notification documentation 2021-06-03 09:00:31 +02:00
drivers ACPICA: Clean up context mutex during object deletion 2021-06-10 13:39:17 +02:00
fs btrfs: tree-checker: do not error out if extent ref hash doesn't match 2021-06-10 13:39:12 +02:00
include net: usb: cdc_ncm: don't spew notifications 2021-06-10 13:39:13 +02:00
init seccomp: Fix CONFIG tests for Seccomp_filters 2021-05-14 09:50:24 +02:00
ipc ipc/mqueue, msg, sem: avoid relying on a stack reference past its expiry 2021-05-26 12:06:54 +02:00
kernel bpf, offload: Reorder offload callback 'prepare' in verifier 2021-06-03 09:00:49 +02:00
lib lib: stackdepot: turn depot_lock spinlock to raw_spinlock 2021-05-22 11:40:55 +02:00
LICENSES LICENSES/deprecated: add Zlib license text 2020-09-16 14:33:49 +02:00
mm mm/hugetlb: fix F_SEAL_FUTURE_WRITE 2021-05-19 10:13:11 +02:00
net mptcp: always parse mptcp options for MPC reqsk 2021-06-10 13:39:16 +02:00
samples samples: vfio-mdev: fix error handing in mdpy_fb_probe() 2021-06-10 13:39:15 +02:00
scripts scripts/clang-tools: switch explicitly to Python 3 2021-06-03 09:00:52 +02:00
security KEYS: trusted: Fix memory leak on object td 2021-05-19 10:12:50 +02:00
sound Revert "Revert "ALSA: usx2y: Fix potential NULL pointer dereference"" 2021-06-03 09:00:51 +02:00
tools perf probe: Fix NULL pointer dereference in convert_variable_location() 2021-06-10 13:39:17 +02:00
usr Merge branch 'work.fdpic' of git://git.kernel.org/pub/scm/linux/kernel/git/viro/vfs 2020-08-07 13:29:39 -07:00
virt Revert "irqbypass: do not start cons/prod when failed connect" 2021-06-03 09:00:34 +02:00
.clang-format RDMA 5.10 pull request 2020-10-17 11:18:18 -07:00
.cocciconfig
.get_maintainer.ignore Opt out of scripts/get_maintainer.pl 2019-05-16 10:53:40 -07:00
.gitattributes .gitattributes: use 'dts' diff driver for dts files 2019-12-04 19:44:11 -08:00
.gitignore kbuild: generate Module.symvers only when vmlinux exists 2021-05-19 10:12:59 +02:00
.mailmap mailmap: add two more addresses of Uwe Kleine-König 2020-12-06 10:19:07 -08:00
COPYING COPYING: state that all contributions really are covered by this file 2020-02-10 13:32:20 -08:00
CREDITS MAINTAINERS: Move Jason Cooper to CREDITS 2020-11-30 10:20:34 +01:00
Kbuild kbuild: rename hostprogs-y/always to hostprogs/always-y 2020-02-04 01:53:07 +09:00
Kconfig kbuild: ensure full rebuild when the compiler is updated 2020-05-12 13:28:33 +09:00
MAINTAINERS f2fs: move ioctl interface definitions to separated file 2021-05-19 10:13:00 +02:00
Makefile Linux 5.10.42 2021-06-03 09:00:52 +02:00
README Drop all 00-INDEX files from Documentation/ 2018-09-09 15:08:58 -06:00

README 

Linux kernel
============

There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.

In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``.  The formatted documentation can also be read online at:

    https://www.kernel.org/doc/html/latest/

There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.

Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.